The Simulation Problem

I’ve been struggling with this problem for a while now every time I sit down to start playing KSP. As you may know, I am a huge space enthusiast, and a stickler for realism when it comes to portraying space and science topics. Then, of course, I also like playing fun video games. So I’m fundamentally at war with myself when I ask myself: how much realism is enough?

The key here is not striving for realism, but making it feel realistic. This means simulating what I know, and glossing over that which I know nothing about. Yes, this is lame. Additionally, there are some things that take far too much effort to simulate realistically — engine physics, weather patterns, n-body gravitation, physiology.

This problem has been eating away at me enough that I haven’t actually been able to play KSP. I tried a variety of different play styles, but ultimately I got stuck on one problem: I wanted my rockets to be as small as possible, and to take the optimal ascent route.

As I began researching this problem, I realized it was not trivial. In fact, planning an ascent path is quite complex, and the equations have a large number of parameters. Another compounding factor was that there is really no good documentation on the internet about ascent patterns. I’m not sure if this is because that information falls under some sort of ITAR restriction, or just because nobody is interested in it. I wasn’t even sure how to start thinking about it. I knew there was something called a “pitch-over maneuver”, but how does it work? Do they pitch over at a constant rate starting at some altitude, or is a more complex function? Are there multiple pitch-over functions? I could find nothing that answered this.

The second problem was that it is not easy to simulate rocket ascents. You have to account for the curvature of the Earth, so it is not a ballistics problem but a set of differential equations in a polar coordinate system. I tried some basic solution in both Scilab (a free version of Matlab) and in Python, but in both cases the complexity of the problem became so great that I threw up my hands before reaching a satisfactory solution. I mean, it’s hard enough if you consider one stage, but once you consider that a rocket can have any number of stages, the design space spirals out of control.

This problem would not stop bothering me. Every time I sat down to play KSP, I realized I was sitting down into a self-imposed math nightmare. Then after that nightmare was solved, I would still be stuck with a inability to truly simulate all the aspects of spaceflight I wanted to simulate, at least not without a lot of work making my own mods.

The moral of the story is: don’t mix realism/math and videogames.

(There is another corollary problem, which is that Reality Is Unrealistic. We have these notions of how phenomenon look drilled into our heads by TV and movies, but the truth is often different and less COOL. Unfortunate that we have been trained to have that heuristic for coolness. TV Tropes says it best. An interesting example is Star Citizen, which shows the ship engines as firing all the time — even when they are off in the physical simulation — because it “looks cool”. Sigh.)